title: Gene regulatory networks elucidating huanglongbing disease mechanisms.
abstract: Next-generation sequencing was exploited to gain deeper insight into the response to infection by Candidatus liberibacter asiaticus (CaLas), especially the immune disregulation and metabolic dysfunction caused by source-sink disruption. Previous fruit transcriptome data were compared with additional RNA-Seq data in three tissues: immature fruit, and young and mature leaves. Four categories of orchard trees were studied: symptomatic, asymptomatic, apparently healthy, and healthy. Principal component analysis found distinct expression patterns between immature and mature fruits and leaf samples for all four categories of trees. A predicted protein - protein interaction network identified HLB-regulated genes for sugar transporters playing key roles in the overall plant responses. Gene set and pathway enrichment analyses highlight the role of sucrose and starch metabolism in disease symptom development in all tissues. HLB-regulated genes (glucose-phosphate-transporter, invertase, starch-related genes) would likely determine the source-sink relationship disruption. In infected leaves, transcriptomic changes were observed for light reactions genes (downregulation), sucrose metabolism (upregulation), and starch biosynthesis (upregulation). In parallel, symptomatic fruits over-expressed genes involved in photosynthesis, sucrose and raffinose metabolism, and downregulated starch biosynthesis. We visualized gene networks between tissues inducing a source-sink shift. CaLas alters the hormone crosstalk, resulting in weak and ineffective tissue-specific plant immune responses necessary for bacterial clearance. Accordingly, expression of WRKYs (including WRKY70) was higher in fruits than in leaves. Systemic acquired responses were inadequately activated in young leaves, generally considered the sites where most new infections occur.
authors.affiliation: Department of Plant Sciences, University of California Davis, Davis, California, United States of America ; Dipartimento di Sistemi Agro-ambientali, Università degli Studi di Palermo, Palermo, Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Martinelli
authors.forename: Russell L
authors.initials: RL
authors.lastname: Reagan
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Uratsu
authors.forename: My L
authors.initials: ML
authors.lastname: Phu
authors.forename: Ute
authors.initials: U
authors.lastname: Albrecht
authors.forename: Weixiang
authors.initials: W
authors.lastname: Zhao
authors.forename: Cristina E
authors.initials: CE
authors.lastname: Davis
authors.forename: Kim D
authors.initials: KD
authors.lastname: Bowman
authors.forename: Abhaya M
authors.initials: AM
authors.lastname: Dandekar
mesh_terms: D002957:Citrus / Q000235:genetics* / Q000382:microbiology; D053263:Gene Regulatory Networks; D010935:Plant Diseases / Q000235:genetics*; D016133:Polymerase Chain Reaction; D059467:Transcriptome